Steered beam antenna systems have been used in defense electronics for radar systems, or for direction finding (DF) applications. These technologies have been making their way into commercial communications, for interference reduction and/or capacity enhancement. The generally accepted term in the latter industry is smart antennas; however, the term has been used to describe many different techniques and technologies. The earlier technologies were based on RF (radio frequency) beam steering, which used selection of one of a number of highly directional antennas. In these technologies, tower top antennas were typically completely passive, with the beams formed via Butler matrices, or by selecting antennas individually. The independent beam signals were then delivered to the base station via separate coaxial RF lines, with signal selection and RF switching performed at the base station.
Digitally adaptive systems, which might use any type of antennas at the tower top, and digital signal processing techniques (DSP) at the base station, have been tested and are slowly making their way into the commercial markets. However, most of these technologies are still based on using passive antennas at the tower top, bringing the RF signals from the tower to the base station via coaxial (RF) cables. The frequency conversion, digital conversion, and beamformer processing is then performed at the base station.
In accordance with one aspect of the invention, an antenna system architecture is based on installing the RF electronics at the tower top, with the antenna or within the antenna housing. Other aspects of the antenna system architecture of the invention include:
Tower top electronics;
Distributed amplifier system;
Frequency and digital conversion at the tower top;
Antenna/array inputs/outputs are time division multiplexed;
Final multiplexed digital signal is converted to fiber optics;
Single or multiple fiber optic delivery cables for backhaul, or convert to microwave for backhaul.
Additionally, this approach allows for a basic split of functionalities, as follows:
RF signal processing is performed at the tower top;
Beamforming (DSP) and channel coding is performed at another location, such as:
a) at the bottom of the tower (base station) or BTS (Base Transceiver System);
b) at the MSC (Mobile Switching Center); or
c) at the CO (Central Switching Office).
This approach allows all processing and software, as well as digital hardware, to be installed at a single location, rather than distributed among various cell sites; which should reduce initial installation costs, as well as maintenance and upgrade costs.
Briefly, in accordance with the foregoing, an antenna system, for tower-top installation, comprises an antenna array comprising an array of Mxc3x97N antenna elements, a corporate feed for operatively interconnecting said antenna elements with a backhaul link for communicating with ground-based equipment, and radio frequency circuits for processing radio frequency signals between said antenna array and said backhaul link, said radio frequency circuits including substantially all of the circuits required for the processing of radio frequencing signals between said array and said backhaul link.